1. Field of the Invention
Aspects of the present invention relate to a wireless communication system, and more particularly, to a cooperative diversity method and apparatus in a wireless communication system.
2. Description of the Related Art
As wireless multimedia services become more common, there is a greater need for wirelessly transmitting high speed information. In order to transmit more information, more frequency bands are needed. However, because there are restrictions on usable frequency bands, a multi-antenna system according to a related art maximizes the transmission capacity of a system in a restricted frequency band.
The multi-antenna system can be divided into a method of increasing a multiplexing gain by increasing a transmission capacity of a channel, and a method of increasing a diversity gain by improving a reliability of a link without reducing a transmission capacity. In particular, the method of increasing the diversity gain uses a multi-antenna to generate a plurality of independent fading channels and obtaining the gain.
Also, an orthogonal frequency division multiple access (OFDMA) method is a parallel type data transmission method using an orthogonality of each subcarrier. The OFDMA method has a high usage efficiency of a frequency, a characteristic appropriate for a multi-channel environment, and a simple structure of a channel compensator. Accordingly, the method of using the multi-antenna and the OFDMA method are selected as basic transmission methods in a system requiring high speed data transmission. Combining the OFDMA method with the multi-antenna system can increase a transmission capacity or reliability of a link.
However, when the multi-antenna is used, a minimum distance between antennas is required to maximize performance. Accordingly, transmission diversity is generally used in only a base station rather than in a terminal. A cooperative diversity technology is provided in order to solve this limitation. The cooperative diversity technology is expected to obtain a diversity gain similar or proportionate to a gain when a multi-antenna is used by binding different and independent mobile phones or terminals and generating a plurality of independent fading channels in each mobile phone or each terminal.
However, a cooperative diversity technology according to a related art has the following problems. First, since an optimum method of selecting a mobile phone or a terminal to be operated in a cooperative diversity mode is not provided in the related art, the diversity gain cannot be maximized. Second, since a wireless resource is additionally allocated for data exchange between terminals to be operated in a cooperative diversity mode according to the related art, an efficiency of a frequency or time resource is reduced.